For many years, researchers have been trying to design computer systems that could efficiently solve what are termed NP problems, which include NP complete and NP hard problems. NP hard problems are problems which are unsolvable within a reasonable amount of time for large input sizes. However, it is sometimes possible to reach approximate solutions. They can be easily solved for small input sizes but they grow exponentially as more variables are added, rendering them unsolvable for modern computers. As a result, many complex problems are solved in parts or using approximations, with the final answer being computationally costly and imprecise. There remains no digital system known to the inventors capable of solving such problems, which therefore are handled in practice via expensive approximations and heuristic methods.
Standard CMOS technology is limited because it can only output the solution bit given the initial input bits. As a consequence, such circuits composed of standard logic gates only operate sequentially.